Chapter 4, Requirements Elicitation

1. Chapter 4, Requirements Elicitation

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3. What does the Customer say?

4. First step in identifying the Requirements: System identification • Two questions need to be answered: • How can we identify the purpose of a system? • What is inside, what is outside the system? • These two questions are answered during requirements elicitation and analysis • Requirements elicitation: • Definition of the system in terms understood by the customer (“Requirements specification”) • Analysis: • Definition of the system in terms understood by the developer (Technical specification, “Analysis model”) • Requirements Process: Contains the activities Requirements Elicitation and Analysis.

5. Techniques to elicit Requirements • Bridging the gap between end user and developer: • Questionnaires:Asking the end user a list of pre-selected questions • Task Analysis:Observing end users in their operational environment • Scenarios: Describe the use of the system as a series of interactions between a concrete end user and the system • Use cases: Abstractions that describe a class of scenarios.

6. Scenario-Based Design Scenarios can have many different uses during the software lifecycle • Requirements Elicitation: As-is scenario, visionary scenario • Client Acceptance Test: Evaluation scenario • System Deployment: Training scenario Scenario-Based Design: The use of scenarios in a software lifecycle activity

7. Types of Scenarios • As-is scenario: • Describes a current situation. Usually used in re-engineering projects. The user describes the system • Example: Description of Letter-Chess • Visionary scenario: • Describes a future system. Usually used in greenfield engineering and reengineering projects • Can often not be done by the user or developer alone • Example: Description of an interactive internet-based Tic Tac Toe game tournament • Example: Description - in the year 1954 - of the Home Computer of the Future.

8. Additional Types of Scenarios (2) • Evaluation scenario: • Description of a user task against which the system is to be evaluated. • Example: Four users (two novice, two experts) play in a TicTac Toe tournament in ARENA. • Training scenario: • A description of the step by step instructions that guide a novice user through a system • Example: How to play Tic Tac Toe in the ARENA Game Framework.

9. How do we find scenarios? • Don’t expect the client to be verbal if the system does not exist • Client understands problem domain, not the solution domain. • Don’t wait for information even if the system exists • “What is obvious does not need to be said” • Engage in a dialectic approach • You help the client to formulate the requirements • The client helps you to understand the requirements • The requirements evolve while the scenarios are being developed

10. Heuristics for finding scenarios • Ask yourself or the client the following questions: • What are the primary tasks that the system needs to perform? • What data will the actor create, store, change, remove or add in the system? • What external changes does the system need to know about? • What changes or events will the actor of the system need to be informed about? • However, don’t rely on questions and questionnairesalone • Insist on task observation if the system already exists (interface engineering or reengineering) • Ask to speak to the end user, not just to the client • Expect resistance and try to overcome it.

11. Scenario example: Warehouse on Fire • Bob, driving down main street in his patrol car notices smoke coming out of a warehouse. His partner, Alice, reports the emergency from her car. • Alice enters the address of the building into her wearable computer , a brief description of its location (i.e., north west corner), and an emergency level. • She confirms her input and waits for an acknowledgment. • John, the dispatcher, is alerted to the emergency by a beep of his workstation. He reviews the information submitted by Alice and acknowledges the report. He allocates a fire unit and sends the estimated arrival time (ETA) to Alice. • Alice received the acknowledgment and the ETA.

12. Observations about Warehouse on Fire Scenario • Concrete scenario • Describes a single instance of reporting a fire incident. • Does not describe all possible situations in which a fire can be reported. • Participating actors • Bob, Alice and John

13. After the scenarios are formulated • Find all the use cases in the scenario that specify all instances of how to report a fire • Example: “Report Emergency“ in the first paragraph of the scenario is a candidate for a use case • Describe each of these use cases in more detail • Participating actors • Describe the entry condition • Describe the flow of events • Describe the exit condition • Describe exceptions • Describe nonfunctional requirements

14. Requirements Elicitation: Difficulties and Challenges • Communicate accurately about the domain and the system • People with different backgrounds must collaborate to bridge the gap between end users and developers • Client and end users have application domain knowledge • Developers have solutiondomain knowledge • Identify an appropriate system (Defining the system boundary) • Provide an unambiguous specification • Leave out unintended features

15. Example of an Ambiguous Specification During a laser experiment, a laser beam was directed from earth to a mirror on the Space Shuttle Discovery The laser beam was supposed to be reflected back towards a mountain top 10,023 feet high The operator entered the elevation as “10023” The light beam never hit the mountain top What was the problem? The computer interpreted the number in miles...

16. Example of an Unintended Feature From the News: London underground train leaves station without driver! • What happened? • A passenger door was stuck and did not close • The driver left his train to close the passenger door • He left the driver door open • He relied on the specification that said the train does not move if at least one door is open • When he shut the passenger door, the train left the station without him • The driver door was not treatedas a door in the source code!

17. Requirements Requirements elicitation Specification :nonfunctional requirements :functional model Analysis :dynamic model :analysis object model Requirements Process :problem statement Analysis Model

18. Requirements Specification vs Analysis Model Both focus on the requirements from the user’s view of the system • The requirements specification uses natural language (derived from the problem statement) • The analysis model uses a formal or semi-formal notation (we use UML)

19. Types of Requirements • Functional requirements • Describe the interactions between the system and its environment independent from the implementation “An operator must be able to define a new game. “ • Nonfunctional requirements • Aspects not directly related to functional behavior. “The response time must be less than 1 second” • Constraints • Imposed by the client or the environment • “The implementation language must be Java “ • Called “Pseudo requirements” in the text book.

20. Functional Requirements Describe user tasks that the system needs to support Phrased as actions “Advertise a new league” “Schedule tournament” “Notify an interest group” Nonfunctional Requirements Describe properties of the system or the domain Phrased as constraints or negative assertions “All user inputs should be acknowledged within 1 second” “A system crash should not result in data loss”. Functional vs. Nonfunctional Requirements

21. Usability Reliability Robustness Safety Performance Response time Scalability Throughput Availability Supportability Adaptability Maintainability Implementation Interface Operation Packaging Legal Licensing (GPL, LGPL) Certification Regulation Types of Nonfunctional Requirements Constraints or Pseudo requirements Quality requirements

22. Nonfunctional Requirements: Examples • “Spectators must be able to watch a match without prior registration and without prior knowledge of the match.” • Usability Requirement • “The system must support 10 parallel tournaments” • Performance Requirement • “The operator must be able to add new games without modifications to the existing system.” • Supportability Requirement

23. What should not be in the Requirements? • System structure, implementation technology • Development methodology • Parnas, How to fake the software development process • Development environment • Implementation language • Reusability • It is desirable that none of these above are constrained by the client. Fight for it!

24. Requirements Validation Requirements validation is a quality assurance step, usually performed after requirements elicitation or after analysis • Correctness: • The requirements represent the client’s view • Completeness: • All possible scenarios, in which the system can be used, are described • Consistency: • There are no requirements that contradict each other.

25. Requirements Validation (2) • Clarity: • Requirements can only be interpreted in one way • Realism: • Requirements can be implemented and delivered • Traceability: • Each system behavior can be traced to a set of functional requirements • Problems with requirements validation: • Requirements change quickly during requirements elicitation • Inconsistencies are easily added with each change • Tool support is needed!

26. We can specify Requirements for “Requirements Management” • Functional requirements: • Store the requirements in a shared repository • Provide multi-user access to the requirements • Automatically create a specification document from the requirements • Allow change management of the requirements • Provide traceability of the requirements throughout the artifacts of the system.

27. Tools for Requirements Management (2) DOORS (Telelogic) • Multi-platform requirements management tool, for teams working in the same geographical location. DOORS XT for distributed teams RequisitePro (IBM/Rational) • Integration with MS Word • Project-to-project comparisons via XML baselines RD-Link (http://www.ring-zero.com) • Provides traceability between RequisitePro & Telelogic DOORS Unicase (http://unicase.org) • Research tool for the collaborative development of system models • Participants can be geographically distributed.

28. Different Types of Requirements Elicitation • Greenfield Engineering • Development starts from scratch, no prior system exists, requirements come from end users and clients • Triggered by user needs • Re-engineering • Re-design and/or re-implementation of an existing system using newer technology • Triggered by technology enabler • Interface Engineering • Provision of existing services in a new environment • Triggered by technology enabler or new market needs

29. Prioritizing requirements • High priority • Addressed during analysis, design, and implementation • A high-priority feature must be demonstrated • Medium priority • Addressed during analysis and design • Usually demonstrated in the second iteration • Low priority • Addressed only during analysis • Illustrates how the system is going to be used in the future with not yet available technology

30. Requirements Analysis Document Template 1. Introduction 2. Current system 3. Proposed system 3.1 Overview 3.2 Functional requirements 3.3 Nonfunctional requirements 3.4 Constraints (“Pseudo requirements”) 3.5 System models 3.5.1 Scenarios 3.5.2 Use case model 3.5.3 Object model 3.5.3.1 Data dictionary 3.5.3.2 Class diagrams 3.5.4 Dynamic models 3.5.5 User interface 4. Glossary

31. How to write a use case (Summary) • Name of Use Case • Actors • Description of Actors involved in use case • Entry condition • “This use case starts when…” • Flow of Events • Free form, informal natural language • Exit condition • “This use cases terminates when…” • Exceptions • Describe what happens if things go wrong • Special Requirements • Nonfunctional Requirements, Constraints

32. Summary • Scenarios: • Great way to establish communication with client • Different types of scenarios: As-Is, visionary, evaluation and training • Use cases • Abstractions of scenarios • Use cases bridge the transition between functional requirements and objects.